A Multimedia Broadcast and Multicast Service (MBMS) can provide a user in a radio cell with a multimedia broadcast and multicast service. In a Long Term Evolution (LTE) system, an MBMS can be provided at both an MBMS-specific frequency layer and a frequency layer shared between an MBMS service and a non-MBMS service. An MBMS-enabled LTE cell may be an MBMS-specific cell or a hybrid MBMS/uni-cast cell. An MBMS service can be transmitted in a single cell or in a plurality of cells.
An MBMS-specific frequency layer refers to a frequency layer dedicated to transmission of an MBMS. When a cell is configured as an MBMS-specific frequency layer, the cell is referred to as an MBMS-specific cell; and when a cell is configured as a frequency layer which is not dedicated to transmission of an MBMS, the cell is referred to as a hybrid MBMS/uni-cast cell in which transmission of uni-cast and MBMS services is coordinated so that an MBMS service is transmitted at some times and a uni-cast service is transmitted at other times. Transmission of an MBMS in a single cell refers to transmission of the MBMS only in the coverage area of a specified cell without any support of MBMS transmission in a plurality of cells in combination, and transmission of an MBMS in plurality of cells requires a support of a transmission mode of Multi Broadcast Single Frequency Network (MBSFN).
The MBSFN refers to synchronous transmission ongoing concurrently in a plurality of cells at the same frequency. The use of this transmission mode can save a resource of frequencies and improve a spectrum utilization ratio. It requires concurrent transmission of the same contents in a plurality of cells. Thus, a receiver of a UE can regard the plurality of MBSFN cells as a large cell. Therefore the UE will both be free of inter-cell interference resulting from transmission in an adjacent cell and benefit from superposition of signals from the plurality of MBSFN cells. The MBSFN transmission mode can be adopted in both an MBMS-specific cell and a hybrid MBMS/uni-cast cell. Furthermore the use of an advanced UE receiver technology can also address the problem of a time difference due to multi-path propagation and hence remove intra-cell interference. A diversity effect resulting from such transmission in a plurality of cells at the same frequency can also address such a problem of covering a blind area, etc., and therefore enhance the reliability of reception and improve a coverage ratio.
Technical characteristics of transmission in a plurality of MBMS cells are as follows.
Firstly synchronous transmission of an MBMS is active in an MBSFN area;
Secondly combined transmission of an MBMS in the plurality of cells is supported;
Thirdly an MBMS point-to-multipoint Traffic Channel (MTCH) and an MBMS point-to-multipoint Control Channel (MCCH) are mapped onto a Multicast Channel (MCH) for Packet Temporary Mobile (PTM) transmission;
Fourthly an MBSFN area can be semi-statically configured, for example, by an Operation and Management (O&M) device, etc.
For transmission of an MBMS in a plurality of cells, a plurality of MCHs can be supported at a carrier frequency. A physical resource of an MCH can be allocated in a pattern of specifying a sub-frame for the MCH, and correlated sub-frames may not necessarily be temporally adjacent. This pattern is referred to as an MCH Sub-frame Allocation Pattern (MSAP). An MSAP of each MCH, over which an MTCH is carried, is signaled over an MCCH, and for an MCH onto which a plurality of MTCHs are mapped, the order in which the respective MTCHs is also signaled over an MCCH. Data of only one MBSFN area is involved over one MCH, but a plurality of MBMS services can be mapped onto each MCH.
The inventors have identified during making of the invention the following technical problem in the prior art:
as can be apparent from above, synchronous transmission of MCCH information in an MBSFN area has to also be ensured in an LTE system in addition to synchronous transmission of MBMS service in the MBSFN area because an MCCH is also mapped onto an MCH.